In TCP/IP that is frequently used as a communication protocol between devices, an IP address is used as information for identifying the device. When the TCP/IP is used, a uniquely determined IP address needs to be allocated to each device on the network.
As a mechanism that automatically provides an IP address to each device on the network, there is a method using a DHCP (Dynamic Host Configuration Protocol). In the DHCP, a device that manages and distributes IP addresses is referred to as a DHCP server, and a device that requests an IP address is referred to as a DHCP client. When being physically connected to the network, the DHCP client transmits an IP-address request packet to the network by broadcast. Upon reception of the IP-address request packet, the DHCP server prepares an IP address for the DHCP client and distributes the IP address to a source device (the DHCP client) via the network (see, for example, Non Patent Literature 1).